“Oh, I just want to change the tub into a shower.”

I hear this very often from potential clients. When considering the options for their bathroom remodels, to most homeowners (and unfortunately way too many tradespeople as well) this sounds like a relatively simple change to make. They understandably but mistakenly think that showers and tubs are more or less the same thing, just different types of bathing areas. They put out water, keep it from splashing all over the place, and send it down a drain. All the plumbing is there, so all it should take is a few small modifications to accommodate a different form factor, right? In truth, here in San Diego, this change is rarely as simple as it sounds if it’s to be done properly.

All national and local Building Codes for many decades have been very clear and should be well known to all professional tradespeople: bathtubs require a 1 ½” diameter drain line, while all showers require a 2″ diameter drain line. There are no exceptions to this code. So, in practice:

Changing an existing shower into a bathtub is simple since the 2″ line is in place and readily accessible a 1 ½ line for the tub can feed into it.

Going from a tub to a shower is not often an easy process since it is a violation of code to run a 2″ line, which is required by the new shower, into a 1 ½” existing tub drain.

The possible ease or probable difficulties that will arise in converting a tub to a shower are completely dependent upon how a home is built and the specific configuration of the existing plumbing in that home. Here in California the majority of homes built since 1970 are slab on grade. Most older homes have perimeter footings, crawl spaces, and wood framed first floors.

Crawl spaces (or basements, which are very uncommon in California) below the first floor of a home make changing a first floor bathroom tub to shower very easy, while slab-on-grade construction can, and often does, require cutting large amounts of concrete and digging 4 to 6 feet deep to reach a main drain large enough to tap into to feed the new 2″ line. Whether a home is single story or multistory can also play a role in how easy it is to connect to a 2″ drain. Existing kitchens, bathrooms or laundries either above or below the bath where you want to convert that have a 2″ drain, can but will not always, make for a relatively easy new 2″ drain connection to those existing drains.

What has been a constant difficult, disappointing, and frightening experience for me in my four decades in this profession is how often I have heard directly from licensed plumbers, and indirectly from homeowners, the following two statements:

Plumber: “Why are you making this project so hard? Just tap the new 2″ line into the 1 ½” line, and hide the connection and the 1 ½” line from the inspector. Or, just don’t get permits. It’s not a big deal!”

Homeowner: “You are the 4th or 5th person I have seen to get a price quote for this project and you are the only one who raised this issue.”

Unfortunately, the majority of those same potential clients ultimately contracted one of those other professionals who either ignored the issue or convinced the client it was not a big deal. Probably because while I make it very clear that I do not care if clients choose to get permits or not for their project as it is their home and they have the right to make that decision, I do not do work that does not meet or exceed building code. Here is why it is a big deal to any homeowner and all professionals who do this work:


For Homeowners: Insurance will not pay for repairs caused by work done in violation of building codes. If you shower backs up because of clogged 1 ½” drain and overflows outside the shower dam, will the insurance pay for the damage? Furthermore, if you sell your home and for any reason the new buyer finds out about the code violation, do you want to be liable for correcting the violations and the necessary repairs they cause?

For Professionals: You are supposed to know better. If things go south on this project for any reason or there is damage or a law suit, you are at the top of the list for liability. Your insurance company will most likely will bail on you, because your actions could be considered fraudulent, and your license could be in jeopardy.

Here I will touch on another topic that I will talk about at much more length in future blog articles: National Building Codes, now under the purview of the IBC. The code I mention above in this article regarding drain size for tubs and showers, has been code for many decades. It is not a bad or illogical code with no justification or science based reasoning, as many of the new codes are. In this article I will not justify the code other than to say, that, in today’s typical home, a shower drain does get clogged much more quickly than a tub drain. And remember that a tub has a dam that is 12″ or more in height, while a typical shower dam is only 0″ to 4″, including today’s ADA showers. In turn, you have far less likelihood of dam overflow and damage to the rest of the home if the drain gets clogged with a tub than you do with a shower. Why I think we need a  Code Change: The single biggest change in our national home construction practices from the time period that this code originated from is the change from basements and crawlspaces below the first floor to the current practice of slab-on-grade construction. In addition to the slab on grade is the more current pre-tensioned and post-tensioned slabs many big builders are using in California for both single and multi-family housing. These slabs are not meant to be cut into for any future changes. Cutting into these slabs seriously compromises the structural integrity of the slab and the home above it. Another change in construction that affects the cost of plumbing today compared to the cost of plumbing decades ago is the advent of Acrylonitrile Butadiene Styrene (ABS) pipes instead of cast iron or copper drains.

Today, the difference in cost between running a 2″ line vs a 1 ½” line to a tub in most new homes would cost less than $20.00 more in material, which would continually come down in price as 1 ½” material goes out of use, with no labor cost difference. To make the code more compatible with current building techniques and possible future innovations, my recommendation would be:

Recommended Code Change:

The minimum size drain feeding any bath tub or shower should be 2″.
I personally would be OK with all fixtures having a 2″ minimum drain. Fixtures with 1 ½” connection like tubs and lavatory sinks, would transition to the 2″ easily. This code change would make new homes more adaptable to future needs and alteration of the home and make drain lines both drain faster and less likely to clog.

Here is an example from our portfolio:

The bathroom in the project referenced here is located on the first floor in a slab on grade built home with no bathroom above it. If there were a bathroom directly above it with a shower in it, the odds are quite high that there would have been a 2″ shower drain coming down through the wall that we could have tapped into for the downstairs bathroom and easily connected to, which is perfectly legal and adherent to building code. Unfortunately, there was no shower or bathroom above this particular bath, as the second-story bathrooms were on the other side of the house, rear, along the outside wall.

I was aware of this potential problem and told the client about it. Upon my survey of the home, I found a clean-out that is for the main sewer line in the garage floor on the other side of the wall between this bath and the garage, about 3 feet into the garage from the sink you see in the pictures. It was pretty obvious that the main sewer line ran from the kitchen and upstairs baths at the rear of the home right under this bath sink and out through the garage to the street sewer connection. I told the client that there most likely would be an additional charge if we needed to jackhammer the floor and dig to that main line to meet code, and added that contingency amount to our contract with a note that the client would get a refund of that amount if that concrete and demo work turned out to be not needed. Upon opening the bath walls and ceiling during construction, we could not find a 2″ line and did need to open the slab about 6 feet laterally to the sink area and dig over 4 feet deep to reach the main line to tap the 2″ shower drain into it. This same bath was the subject of another issue and blog entry dealing with venting.